Concept: The correct word should mean “to increase or add to” something, like monthly earnings.Explanation:The sentence discusses adding a specific amount to the monthly earnings.“Expand” and “enlarge” usually refer to size or scope, not income.“Complete” means to finish or make whole, which does not fit here.“Augment” means to increase something by adding to it.Therefore, “augment” best completes the sentence.Answer: D. augment